For a 1992 BMW 525I do you have to use premium gas or can you use regular and what would be the consequences?

I've been using regular unleaded in my '92 525i for about the last 2 years ever since the gas crunch and it has been running pretty well. I honestly haven't been able to tell much of a difference, maybe just a tiny bit of sluggishness. It's worth it to me, but probably not to most.